After adding Subsurf modifier, some UV is distorted
Using subsurface modifier will not 100% guarantee that has perfect uv result. I already told in comment, however if you want to add more geometry after finish modeling, should be careful to not messing up the UV to watch carefully while adding additional geometry.

This especially messing up that adding more edges in curved geometry, so it's just better to remap your UV to new Geometry.

If you using Substance Painter for creating texture, don't be afraid, the program will automatically repaint all your previous works even the geometry and UV's are changed(but not 100%).